The present invention relates to material handling apparatus and particularly to a control system for the fine vertical and horizontal positioning of a vehicle with respect to a storage location in the system.
In warehousing system where vehicles are employed for transporting articles and materials into and out of storage locations located in an array of storage bins, a variety of positioning means have been employed. Such systems include, for example, shaft encoders which provide pulses the number of which represent the distance a vehicle has traveled from a reference location such that by counting the number of pulses, the position of a vehicle can be coarsely estimated.
More accurate alignment systems include target means such as a retroreflective strip positioned on the materials storage rack at a predetermined location, and one or more light sensors positioned on the movable vehicle and aligned with the target when the vehicle is aligned in an operative position with respect to a storage location. Such systems may include more than a single sensor to provide a greater degree of accuracy in the control. U.S. Pat. No. 3,824,020, for example, represents one such system where vertical positioning of a material handling apparatus is controlled using a plurality of light sensors positioned in a line to provide relatively accurate alignment of the vehicle in a single direction. Also, a system has been proposed in which four detectors are arranged in a square pattern skewed at 45.degree. to provide for the centering alignment of a conveyor device with respect to a target.